Had the same problem with my pixel 5a. The Tesla service guy spent 2 hours and final figured out that the default BT version on the phone (1.5) needs to be changed to 1.6. you need to be in developer mode to make the change.I have tested my phone (Pixel 5) with and without Tesla app in the background. I even reboot my phone with no apps in background to be sure. I can confirm that it makes NO difference, at least for my phone. It worked fine either way as the car key.